What other catalysts do you see, going forward? ... What do you see near term, that might increase demand for brkb common?

One possible answer: Same old.
Weak mean reversion of price in the direction of what it's actually worth.
The value rises, the price eventually tags along, with wandering along the way.
At some point a cheap stock will be perceived as cheap and people, at the margin, will want to own more shares and bid up the price a bit.
This mechanism certainly has no firm time frame, but no other "catalyst" is really needed.

As for Apple and China and Taiwan and lions and tigers and bears oh my...I agree it's a big risk.
But it's bounded.
I estimate Apple accounts for around 1/5 of the value of a Berkshire share.
Apple's presence in greater China (production and sales) might be critical for (say) half of the value of a share of Apple.
(Leaving "hard" would be an even bigger hit for a while, but there would be substantial if not complete recovery over time, so some of it is only a one-time loss)
So, round numbers, the worst downside risk to the value of a share of Berkshire is on the order of 10% from this particular concern.
That would be very bad, but survivable.
I've permanently lost 10% of my portfolio before, and life goes on: there's enough left for it to recover and hit new highs again.

Jim